This invention relates to an inkjet recording element. More particularly, this invention relates to an ink jet recording element containing coated particles.
In a typical ink jet recording or printing system, ink droplets are ejected from a nozzle at high speed towards a recording element or medium to produce an image on the medium. The ink droplets, or recording liquid, generally comprise a recording agent, such as a dye or pigment, and a large amount of solvent. The solvent, or carrier liquid, typically is made up of water, an organic material such as a monohydric alcohol, a polyhydric alcohol or mixtures thereof.
An inkjet recording element typically comprises a support having on at least one surface thereof an ink-receiving or image-forming layer, and includes those intended for reflection viewing, which have an opaque support, and those intended for viewing by transmitted light, which have a transparent support.
While a wide variety of different types of image-recording elements for use with ink jet devices have been proposed heretofore, there are many unsolved problems in the art and many deficiencies in the known products which have limited their commercial usefulness.
It is well known that in order to achieve and maintain photographic-quality images on such an image-recording element, an ink jet recording element must:
Be readily wetted so there is no puddling, i.e., coalescence of adjacent ink dots, which leads to non-uniform density
Exhibit no image bleeding
Exhibit the ability to absorb high concentrations of ink and dry quickly to avoid elements blocking together when stacked against subsequent prints or other surfaces
Exhibit no discontinuities or defects due to interactions between the support and/or layer(s), such as cracking, repellencies, comb lines and the like
Not allow unabsorbed dyes to aggregate at the free surface causing dye crystallization, which results in bloom or bronzing effects in the imaged areas
Have an optimized image fastness to avoid fade from contact with water or radiation by daylight, tungsten light, or fluorescent light
An ink jet recording element that simultaneously provides an almost instantaneous ink dry time and good image quality is desirable. However, given the wide range of ink compositions and ink volumes that a recording element needs to accommodate, these requirements of ink jet recording media are difficult to achieve simultaneously.
Ink jet recording elements are known that employ porous or non-porous single layer or multilayer coatings that act as suitable image receiving layers on one or both sides of a porous or non-porous support. Recording elements that use non-porous coatings typically have good image quality but exhibit poor ink dry time. Recording elements that use porous coatings typically contain colloidal particulates and have poorer image quality but exhibit superior dry times.
While a wide variety of different types of porous image-recording elements for use with ink jet printing are known, there are many unsolved problems in the art and many deficiencies in the known products which have severely limited their commercial usefulness. The challenge of making a porous image recording layer is to achieve a high gloss level without cracking, high color density, and a fast drying time.
U.S. Pat. No. 5,576,088 relates to an ink jet recording element wherein a gloss providing layer containing an inorganic filler and a latex is coated on top of an ink receiving layer. However, there is a problem with this element in that the drying time is slow and there is a tendency for the layer to exhibit cracks.
U.S. Pat. No. 5,912,071 relates to a recording medium comprising a substrate and a porous layer formed on the substrate wherein the porous layer comprises water insoluble resin particles preferably having a core/shell structure. However, there is no reference to the physical properties of the particles.
U.S. Pat. No. 6,099,956 relates to a recording medium comprising a support with a receptive layer coated thereon. The receptive layer comprises a water insoluble polymer that is preferably a copolymer comprising a styrene core with an acrylic ester shell. However, there is no reference to the physical properties of the particles.
It is an object of this invention to provide an ink jet recording element that has a fast ink dry time. It is another object of this invention to provide an ink jet recording element that has good image quality.
These and other objects are achieved in accordance with the invention which comprises an inkjet recording element comprising a substrate having thereon an image-receiving layer comprising a filler and coated particles comprising a polymeric hard core-polymeric soft shell, the Tg of the polymeric hard core material being greater than about 60xc2x0 C., the Tg of the polymeric soft shell material being less than about 100xc2x0 C., and the filler being present in the image-receiving layer in an amount of from about 50 to about 95% by weight, the substrate being paper, resin-coated paper, synthetic paper, impregnated paper, cellulose acetate or a polyester film.
The ink jet recording element of the invention provides a fast ink dry time and good image quality.
As noted above, the substrate used in the invention may be porous such as paper or non-porous such as resin-coated paper; synthetic paper, such as Teslin(copyright) or Tyvek(copyright); an impregnated paper such as Duraform(copyright); cellulose acetate or polyester films. The surface of the substrate may be treated in order to improve the adhesion of the image-receiving layer to the support. For example, the surface may be corona discharge treated prior to applying the image-receiving layer to the support. Alternatively, an under-coating or subbing layer, such as a layer formed from a halogenated phenol or a partially hydrolyzed vinyl chloride-vinyl acetate copolymer, can be applied to the surface of the support. The papers listed above include a broad range of papers, from high end papers, such as photographic paper to low end papers, such as newsprint. In a preferred embodiment, Ektacolor paper made by Eastman Kodak Co. is employed.
The support used in the invention may have a thickness of from about 50 to about 500 xcexcm, preferably from about 75 to 300 xcexcm. Antioxidants, antistatic agents, plasticizers and other known additives may be incorporated into the support, if desired.
As described above, the image-receiving layer of the invention contains a filler. Any filler may be used in the invention, such as a metal oxide, metal hydroxide, calcium carbonate, barium sulfate, clay or organic particles such as polymeric beads. Examples of organic particles useful in the invention are disclosed and claimed in U.S. patent application Ser. Nos. 09/458,401, filed Dec. 10, 1999; 09/608,969, filed Jun. 30, 2000; 09/607,417, filed Jun. 30, 2000; 09/608,466 filed Jun. 30, 2000; 09/607,419, filed Jun. 30, 2000; and 09/822,731, filed Mar. 30, 2001; the disclosures of which are hereby incorporated by reference. In a preferred embodiment of the invention, the metal oxide is silica, alumina, zirconia or titania. In another preferred embodiment of the invention, the particle size of the filler is from about 5 nm to about 5000 nm. In still another preferred embodiment of the invention, the filler is present in an amount of from about 50 to about 95% by weight of materials present in the image-receiving layer.
In a preferred embodiment of the invention, the coated particles comprising a polymeric hard core-polymeric soft shell comprises polymeric particles having a core of material having a relatively high Tg which is coated with another polymer having a lower Tg. The coated particles used in the invention may be prepared by emulsion polymerization as described in xe2x80x9cEmulsion Polymerization and Emulsion Polymersxe2x80x9d, edited by P. A. Lovell and M. S. El-Aassar, John Wiley and Sons, 1997. For example, the coated particles is by adsorption of prepared by polymerizing a monomer in the presence of the polymeric hard core material. Another technique for preparing the coated particles is by adsorption of the polymeric soft shell material onto the surface of the polymeric hard core material. Still another technique for preparing the coated particles is by forming chemical bonds between the polymeric hard core material and the polymeric soft shell material.
Any polymeric material may be used as the polymeric hard core of the coated particles of the invention, such as poly(methylmethacrylate), poly(styrene), poly(p-methylstyrene), poly(t-butylacrylamide), poly(styrene-co-methylmethacrylate), poly(styrene-co-t-butylacrylamide), poly(methylmethacrylate-co-t-butylacrylamide), and homopolymers derived from p-cyanophenyl methacrylate, pentachlorophenyl acrylate, methacrylonitrile, isobomyl methacrylate, phenyl methacrylate, acrylonitrile, isobomyl acrylate, p-cyanophenyl acrylate, 2-chloroethyl acrylate, 2-chloroethyl methacrylate, 2-naphthyl acrylate, n-isopropyl acrylamide, 1-fluoromethyl methacrylate, isopropyl methacrylate, and 2-hydroxypropyl methacrylate. In a preferred embodiment of the invention, the polymeric material comprises particles of poly(methyl-methacrylate), polystyrene, poly(p-methylstyrene), poly(t-butylacrylamide) or poly(styrene-co-methyhnethacrylate). In another preferred embodiment of the invention, the particle size of the polymeric particles is from about 5 nm to about 1000 nm. In yet another preferred embodiment of the invention, the Tg of the polymeric particle is at least about 60xc2x0 C., preferably from about 60xc2x0 C. to about 150xc2x0 C.
The polymeric soft shell material employed in the invention has a Tg of less than about 100xc2x0 C., preferably from about xe2x88x9250xc2x0 C. to about 65xc2x0 C. Methods for determining Tg values of organic polymers are described in xe2x80x9cIntroduction to Physical Polymer Sciencexe2x80x9d, 2nd Edition by L. H. Sperling, published by John Wiley and Sons, Inc., 1992. For each of the organic polymers in Table 1 below, the Tg value was calculated as the weighted sum of the Tg values for homopolymers derived from each of the individual monomers, i, that make up the polymer:       T    ⁢          xe2x80x83        ⁢    g    =            ∑      i        ⁢                  W        i            ⁢              X        i            
where W is the weight percent of monomer i in the organic polymer, and X is the Tg value for the homopolymer derived from monomer i. Tg values for the homopolymers were taken from xe2x80x9cPolymer Handbookxe2x80x9d, 2nd Edition by J. Brandrup and E. H. Immergut, Editors, published by John Wiley and Sons, Inc., 1975.
In a preferred embodiment of the invention, monomers used to prepare the polymeric soft shell material include acrylate and styrene monomers which may have a cationic, anionic, or nonionic functionality such as quaternary ammonium, pyridinium, imidazolium, sulfonate, carboxylate or phosphonate groups. Examples of useful monomers include: n-butyl acrylate, n-ethylacrylate, 2-ethylhexylacrylate, methoxyethylacrylate, methoxyethoxy-ethylacrylate, ethoxyethylacrylate, ethoxyethoxyethylacrylate, 2-ethylhexyl methacrylate, n-propylacrylate, hydroxyethylacrylate, etc. and cationic monomers such as a salt of trimethylammoniumethyl acrylate and trimethylammoniumethyl methacrylate, a salt of triethylammoniumethyl acrylate and triethylammoniumethyl methacrylate, a salt of dimethylbenzylammoniumethyl acrylate and dimethylbenzylammoniumethyl methacrylate, a salt of dimethylbutylammoniumethyl acrylate and dimethylbutylammoniumethyl methacrylate, a salt of dimethylhexylammoniumethyl acrylate and dimethylhexylammoniumethyl methacrylate, a salt of dimethyloctylammoniumethyl acrylate and dimethyloctylammoniumethyl methacrylate, a salt of dimethyldodeceylammoniumethyl acrylate and dimethyldocecylammoniumethyl methacrylate, a salt of dimethyloctadecylammoniumethyl acrylate and dimethyloctadecylammoniumethyl methacrylate, etc. Salts of these cationic monomers that can be used include chloride, bromide, methylsulfate, triflate, etc.
Examples of these polymeric soft shell materials include poly(n-butylacrylate-co-vinylbenzyltriimethylammonium chloride), poly(n-butylacrylateco-vinylbenzyltrimethylammonium bromide), poly(n-butylacrylate-co-vinylbenzyldimethylbenzylammonium chloride) and poly(n-butylacrylate-co-vinylbenzyldimethyloctadecylammonium chloride). In a preferred embodiment of the invention, the polymeric soft shell material can be poly(n-butyl acrylate), poly(2-ethylhexyl aclylate) poly(methoxyethylacrylate), poly(ethoxyethylacrylate), poly(n-butylacrylate-co-trimethylarnmoniumethyl acrylate), poly(n-butylacrylate-co-trimethylammoniumethyl methacrylate) or poly(n-butylacrylate-co-vinylbenzyltrimethylammonium chloride).
Any weight ratio of the polymeric hard core material to the polymeric soft shell material can be used. Preferably, the weight ratio of the polymeric hard core material to the polymeric soft shell material is from about 0.2:1 to about 20:1.
Following are examples of coated particles of polymeric soft shell-polymeric hard core materials that can be used in the invention:
In a preferred embodiment of the invention, the coated particles comprise up to about 50 wt. % of the image-receiving layer.
The image-receiving layer of the invention may also contain a polymeric binder in an amount insufficient to alter its porosity. In a preferred embodiment, the polymeric binder is a hydrophilic polymer, such as poly(vinyl alcohol), poly(vinyl pyrrolidone), gelatin, cellulose ethers, poly(oxazolines), poly(vinylacetamides), partially hydrolyzed poly(vinyl acetate/vinyl alcohol), poly(acrylic acid), poly(acrylamide), poly(alkylene oxide), sulfonated or phosphated polyesters and polystyrenes, casein, zein, albumin, chitin, chitosan, dextran, pectin, collagen derivatives, collodian, agar-agar, arrowroot, guar, carrageenan, tragacanth, xanthan, rhamsan and the like; or a low Tg latex such as poly(styrene-co-butadiene), a polyurethane latex, a polyester latex, poly(n-butyl acrylate), poly(n-butyl methacrylate), poly(2-ethylhexyl acrylate), a copolymer of n-butylacrylate and ethylacrylate, a copolymer of vinylacetate and n-butylacrylate, etc. The polymeric binder should be chosen so that it is compatible with the aforementioned particles.
The amount of binder used should be sufficient to impart cohesive strength to the ink jet recording element, but should also be minimized so that the interconnected pore structure formed by the aggregates is not filled in by the binder. In a preferred embodiment of the invention, the weight ratio of the binder to the total amount of particles is from about 1:20 to about 1:5.
In order to impart mechanical durability to an ink jet recording element, crosslinkers which act upon the binder discussed above may be added in small quantities. Such an additive improves the cohesive strength of the layer. Crosslinkers such as carbodiimides, polyfunctional aziridines, aldehydes, isocyanates, epoxides, polyvalent metal cations, and the like may all be used.
To improve colorant fade, UV absorbers, radical quenchers or antioxidants may also be added to the image-receiving layer as is well known in the art. Other additives include pH modifiers, adhesion promoters, rheology modifiers, surfactants, biocides, lubricants, dyes, optical brighteners, matte agents, antistatic agents, etc. In order to obtain adequate coatability, additives known to those familiar with such art such as surfactants, defoamers, alcohol and the like may be used. A common level for coating aids is 0.01 to 0.30 wt. % active coating aid based on the total solution weight. These coating aids can be nonionic, anionic, cationic or amphoteric. Specific examples are described in MCCUTCHEON""s Volume 1: Emulsifiers and Detergents, 1995, North American Edition.
An ink jet coating may be applied to one or both substrate surfaces through conventional pre-metered or post-metered coating methods such as blade, air knife, rod, roll coating, etc. The choice of coating process would be determined from the economics of the operation and in turn, would determine the formulation specifications such as coating solids, coating viscosity, and coating speed.
The image-receiving layer thickness may range from about 1 to about 60 xcexcm, preferably from about 5 to about 40 xcexcm.
In addition to the image-receiving layer, the recording element may also contain a base layer, next to the support, the function of which is to absorb the solvent from the ink. Materials useful for this layer include inorganic particles and polymeric binder.
In addition to the image-receiving layer, the recording element may also contain a layer on top of the image-receiving layer, the function of which is to provide gloss. Materials useful for this layer include sub-micron inorganic particles and/or polymeric binder.
After coating, the ink jet recording element may be subject to calendering or supercalendering to enhance surface smoothness. In a preferred embodiment of the invention, the inkjet recording element is subject to hot, soft-nip calendering at a temperature of about 65xc2x0 C. and a pressure of 14000 kg/m at a speed of from about 0.15 m/s to about 0.3 m/s.
Ink jet inks used to image the recording elements of the present invention are well-known in the art. The ink compositions used in ink jet printing typically are liquid compositions comprising a solvent or carrier liquid, dyes or pigments, humectants, organic solvents, detergents, thickeners, preservatives, and the like. The solvent or carrier liquid can be solely water or can be water mixed with other water-miscible solvents such as polyhydric alcohols. Inks in which organic materials such as polyhydric alcohols are the predominant carrier or solvent liquid may also be used. Particularly useful are mixed solvents of water and polyhydric alcohols. The dyes used in such compositions are typically water-soluble direct or acid type dyes. Such liquid compositions have been described extensively in the prior art including, for example, U.S. Pat. Nos. 4,381,946; 4,239,543 and 4,781,758, the disclosures of which are hereby incorporated by reference.
Although the recording elements disclosed herein have been referred to primarily as being useful for ink jet printers, they also can be used as recording media for pen plotter assemblies. Pen plotters operate by writing directly on the surface of a recording medium using a pen consisting of a bundle of capillary tubes in contact with an ink reservoir.
The following examples further illustrate the invention.